1. Field of the Invention
This invention relates to processes for finishing glass surfaces, and more particularly for the finishing of the surfaces of glass articles to close tolerances and a brilliant blemish-free state.
2. Description of the Prior Art
The shaping and finishing of glass articles to close tolerances are conventionally carried out by the operations referred to as grinding or diamond machining and subsequent polishing. The term "grinding" conventionally refers to the shaping of the glass surface by abrasives to a desired contour and polishing refers to the application of the finish to the surface. Polishing is usually effected mechanically, using a shaped tool known as a polishing lap, which is normally rotated and works on the glass surface through the intermediary of inert fine solid particles suspended in a liquid supplied to the lap or to the glass surface so as to prevent direct contact between the lap and the glass surface. Grinding and mechanical polishing are the operations which are conventionally used in converting glass articles into lenses for optical and opthalmic purposes with a particular precise contour and polished finish.
The use of chemical attack as a means of polishing and cleaning the surfaces of glass articles is well known and is used for example in the finishing of lead crystal glass which has been cut to provide a decorative surface on the glass. The possibility of using chemical attack as a means of surfacing a continuous ribbon of glass, or of surfacing a face of a sheet of glass, has been disclosed and described in U.K. Patent Specifications Nos. 747,738, 747,759 and 892,607 in the name of Pittsburgh Plate Glass Company. These specifications describe the use of a chemical solution to attack the glass surface, the solution consisting of a solvent, an acid capable of supplying hydrogen ions when dissolved in said solvent, a fluoride soluble in said solution, said fluoride having a cation from the group of organic and inorganic radicals capable of forming a silicofluoride or a fluoride that is highly insoluble in the solvent, and a suppressant to further increase the insolubility of the silicofluoride or fluoride in said solvent in order to control the size of the particles formed at the surface. The solution reacts with the glass surface and a masking film is formed which prevents further reaction with the glass surface until the film is removed. The reaction products are continuously removed mechanically by abrasion with a polishing lap so as to re-expose the high portions of the glass surface to attack until a desired shape is obtained. The surface is then flooded with water. The processes disclosed and described as surfacing in the above U.K. patent specifications, however, relate to carrying out a uniform polishing action on a flat surface in which the amount of glass removed is kept to a minimum.
It is over twenty years since the publication of U.K. Specifications 747,738 and 747,759 and we are unaware of any large scale application of the techniques described, either to the finishing of flat glass or to that of any other articles.